backwasher

A backwasher is a horizontal rotating drum or trough machine that agitates carded wool immersed in water and soap solution to remove dirt, grease, and other contaminants introduced during carding. The carded web enters as a loose, fluffy mat and exits after rinsing and partial dewatering, ready for drying. The term appears in textile mills where the carding process, which opens and aligns fibres, simultaneously traps trash particles and residual lanolin that must be removed before combing or spinning.

The machine operates at relatively low speeds (typically 20-40 revolutions per minute) to avoid felting the delicate carded wool. Water temperature is controlled, usually between 40-50 degrees Celsius, since excessive heat or mechanical agitation can cause the fibres to mat irreversibly. The drum or agitator design prevents pooling of dirt by keeping the wool in continuous motion throughout the wash tank. Some machines use multiple compartments for wash, rinse, and soapy rinse stages in sequence.

Variants and placement in the process

Backwashers are distinct from other wool washers used earlier in the sequence, such as scour machines that clean raw fleece before carding. The backwasher sits downstream of the card, working on already-separated fibres rather than on intact fleece locks. It can handle the fragile, tangled form of carded wool without the heavy mechanical action needed for raw fibres. In some mills, especially those working with recycled or heavily contaminated wool, a backwasher is essential; in others, particularly those using clean, pre-scoured wool tops, it may be bypassed.

The name reflects its position in the sequence: it performs washing that comes after the back (or carding engine), using historical terminology where textile machines were often referred to by their function or position in the line. The word is primarily British; North American mills may use terms like post-card washer or carded wool washer.

Common issues include uneven washing when carded wool bunches rather than remaining dispersed, excessive moisture retention if squeeze or press rollers are worn, and corrosion of the drum or internals from acidic or salt-laden rinse water. Regular inspection of drain systems is necessary because trapped lint can clog outlets and cause waterlogging. The energy cost is significant in mills running continuous backwashing: heating and pumping water for multiple wash and rinse cycles contributes measurably to production cost.